[Tom Machum]

Tom Machum on October 21, 2020 at 4:35 am #20263

Hi Steve,
Thanks for the reply! The damper is the Parker Hannifin or Cleveland 15-10 model, which is the replacement for the original Piper PN 456-017 . There is also a rebuild kit for the 15-10, which was installed at last annual. At that time we also checked all of the items you mentioned in your reply, and all seemed to be fine.

Given that the pulsing seems worse in the right pedal, maybe swapping the bungee assemblies may provide a clue? Also, any leads on a source for the bungees? Piper PN 35262-02; they’re expensive too!

Help! ::P:

[STEVE]

STEVE on October 20, 2020 at 10:42 am #20260

Hi Tom;
The following causes are listed in the service manual:
1) worn steering horn bolt holes
2) excessive free play in steering bungees
3) shimmy dampener or bracket loose at mounting
4) nose tire out of balance
5) worn or loose wheel bearings
6) worn torque link bolts or bushings.
7) improper nose gear fairing.
I suggest you balance the nose wheel/tire assembly. When you re install the balanced assembly, make sure the wheel bearings are not loose.
There is also a Piper service bulletin (SB 1242A) that calls for an inspection of cracks at the welds of the rudder bar assembly. Although your Dakota is not listed in the applicability paragraph, it wouldn’t hurt to take a good look at the welds for cracks and breakage in these assemblies.
Have you or your mechanic removed the shimmy dampener and physically pushed and pulled on it to see if it fully dampens in both directions?? If it doesn’t then that’s a contributing factor.
In the past Piper shimmy dampeners could not be rebuilt. The parts book I have says the shimmy dampener is a 456 017 (PS50152-7). Plane Parts sells an inexpensive kit to rebuild that dampener. https://www.planepartsinc.com/store/456-017-piper-shimmy-damper-kit/.
However, you write that you replaced your shimmy dampener with a new one from Parker Hannifan. Does it have a part number, or was a part number entered in the maintenance records when it was installed??
Steve

[Tom Machum]

Tom Machum on October 16, 2020 at 4:42 am #20257

Hi!
I’m partners in a ’79 PA-28-236 and we’ve been having off and on nosewheel shimmies on landing, predominantly when applying brakes. It seems worst at lower speeds in the landing roll; for example, if you apply brakes at higher speeds it’s initially OK, then it starts to shimmy and if you keep the brakes applied, it gets progressively worse so brakes are released and then reapplied with some shimmy, the process is repeated, and then the shimmy disappears altogether below maybe 15kts or so.

Various techniques have been experimented with by varying back pressure on the column to take weight off the nose. No success.

Again, it only seems to happen when applying brakes and it seems worse in the right pedal. We have checked all tires for round, played with nosewheel tire pressure (up to max and then down in increments), checked rotors (pads are quite new) and everything seems fine; we even rotated the main wheel assemblies to the opposite sides, but the shimmy hasn’t changed.

About 9 years ago the damper was replaced with the Parker Hannifin model (very expensive) and it seemed to do the trick until a few years ago when the shimmy started up again. We rebuilt the damper about 50hrs ago and checked all linkages for play, etc. and that seemed to help for a bit, but it’s baaack LOL

I’ve read elsewhere online to check rudder cable tension, we’ve not done this yet. We are considering a second rebuild of the damper as a new one is several thousands of dollars!

Any ideas? Thanks!